chore(nli): PR #176 회차 1 리뷰 반영

- lib.rs::NliScores::faithfulness doc 의 `rag.nli_faithfulness_min` → `rag.nli_threshold` (spec §2.5/§2.6 의 실 config knob 이름 정합).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/kebab-nli/src/lib.rs

@@ -25,7 +25,7 @@ pub struct NliScores {
 
 impl NliScores {
     /// Faithfulness score = entailment channel. The rag crate compares this
-    /// against `rag.nli_faithfulness_min` to decide whether to refuse.
+    /// against `rag.nli_threshold` to decide whether to refuse.
     pub fn faithfulness(&self) -> f32 {
         self.entailment
     }